Process for transalkylating benzene and dialkylbenzene

ABSTRACT

Benzene and dialkylbenzene are transalkylated to alkylbenzene by contact at temperatures of 175° C. to 450° C. with a novel siliceous composition prepared by impregnating porous silica with aluminum hydride and subsequently heating the impregnated silica to a temperature of from about 300° C. to about 900° C. in a non-oxidizing environment.

This application is a continuation-in-part of application Ser. No.219,279, filed Dec. 22, 1980, now U.S. Pat. No. 4,335,022, which is acontinuation-in-part of application Ser. No. 061,205, filed July 27,1979, now abandoned.

FIELD OF THE INVENTION

This invention relates to a process for transalkylation of benzene anddialkyl benzene utilizing as catalysts novel siliceous compositionsprepared by reacting porous silica with aluminum hydride.

BACKGROUND OF THE INVENTION

Aluminum hydride has been decomposed to produce aluminum metal coatingson glass objects in U.S. Pat. No. 3,501,333, issued Mar. 17, 1970. Theprocesses are typically low temperature processes, below 250° C. Theinstant compositions contain no aluminum metal.

U.S. Pat. No. 3,146,209, issued Aug. 25, 1964, teaches a method forproducing an aluminum hydride containing silica in which bound watermolecules on the silica surface are replaced with aluminum hydridemolecules to provide a solid composition basically comprising silica anda hydride source attached thereto. There is no teaching in thisreference of any subsequent treatment being applied to their gelmaterial to produce an oxide material comparable to the instantcompositions.

U.S. Pat. No. 3,305,590, issued Feb. 21, 1967, discloses a generalprocess for making alumino-silicates. This reference generally teachesimpregnation of silica with any decomposable aluminum salt. The aluminumhydride used to prepare the instant composition is not considered a saltbut rather is a covalent compound (see Metal Hydrides, Mueller et al.,p. 545, Academic Press, 1968).

SUMMARY OF THE INVENTION

Benzene and dialkylbenzene are transalkylated to alkylbenzene by contactwith catalysts comprising unique siliceous materials which are preparedby impregnating porous silica with solutions of aluminum hydride andsubsequently heating the impregnated silica in a non-oxidizingenvironment to temperatures of from about 300° to about 900° C. Thetransalkylation reaction is typically carried out at temperaturesranging from about 175° C. to about 450° C.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The porous silicas used in the preparation of the instant compositionare readily available commercially and are known as silica gels whichare essentially substantially dehydrated amorphorous silica. Thesematerials are available in various density grades, from low density withsurface areas ranging from about 100-200 m² /g, to regular density withsurface areas up to about 800 m² /g. These commercially availablematerials are used as desiccants, selective adsorbents, catalysts andcatalyst supports. The porous silica may contain minor proportions ofother materials without departing from the scope of the invention suchas for example alumina and carbon. Prior to use the porous silica shouldbe substantially free of adsorbed water, i.e. "substantiallydehydrated". The residuum of chemically bound water, i.e. water ofhydration, is not harmful to the process of this invention. The adsorbedor free water is removed by heating the porous silica at temperaturesfrom about 200° to about 900° C. prior to contact with the aluminumhydride impregnating solution. Any environment that will provide fordrying is suitable, such as air, vacuum, inert gas such as nitrogen,etc. The dried porous silica should be kept away from a humid atmosphereafter drying. A convenient drying atmosphere is that used to heat theimpregnated silica, such as nitrogen.

The aluminum hydride suitable for use in preparing the catalysts used inthis invention is prepared commercially by reacting at room temperaturelithium aluminum hydride and aluminum chloride in diethyl ether (Et₂ O).The product is isolated in high yield by decanting and drying at roomtemperature. The product is analyzed as AlH₃.1/3Et₂ O. For purposes ofthis invention the aluminum hydride is dissolved in a suitable organicsolvent. The prime requirement on the solvent is that it be anhydrousand non-hydroxyl containing since water and alcohol react with aluminumhydride. Suitable solvents are for example, ethers, such as diethylether, tetrahydrofuran, pyridine, benzene, toluene, chloroform and thelike.

To prepare the compositions used in the instant invention, porous silicasuitably dried of adsorbed water is contacted with a solution ofaluminum hydride in appropriate proportions as to provide the desiredamount of aluminum hydride per unit weight of silica. A suitable methodof impregnation is described in U.S. Pat. No. 3,146,209, issued Aug. 25,1964. The impregnated silica is dried of solvent and then heated(activated) in a non-oxidizing atmosphere at temperatures from about300° C. to about 900° C., more preferably at temperatures of from about450° C. to about 750° C. The drying step is preferably carried out inthe initial stages of the heating step. Suitable non-oxidizingatmospheres are inert atmospheres such as nitrogen, helium, argon,vacuum, etc; and reducing atmospheres such as hydrogen, carbon monoxide,etc. Drying temperatures are not critical and depend on the particularsolvent and will range from about 60 to about 100% of the boiling point(absolute). Drying and heating times are not critical and depend upontemperatures. They are readily determined by simple experimentation.Five minutes to one hour are usually sufficient. Typically the amount ofaluminum hydride (measured as aluminum metal) added will range fromabout 0.01 to about 35, preferably from about 0.1 to about 25 and morepreferably from about 1 to about 10 percent by weight of the totalcomposition. Different reactions will require different optimum amountsof aluminum hydride added. For example, for dehydrocoupling ofisobutenes to aromatics the aluminum hydride added will range from about2 to about 10 percent by weight of aluminum per total weight ofcomposition.

The instant compositions find use for catalyzing acid catalyzedreactions. The instant compositions are acidic as compared to theessentially neutral silicas. The instant composition are similar inacidity to the acidic binary alumina-silica gels. While the exactphysical structure of the instant composition is not known, it isspeculated that the decomposition of the aluminum hydride on the silicasurface produces localized Lewis acid sites having an atomic ratio ofoxygen to metal ratios lower than the normal oxygen to silica ratio.Analysis of the instant composition indicated no aluminum metal had beendeposited on the surface and an insignificant amount of residualaluminum hydride remained. These findings are consistent with the abovetheory of aluminum hydride reacting with the silica.

The instant compounds prepared using the covalent aluminum hydridecompounds differ significantly in their physical characteristic whencompared to compounds prepared using decomposable salts. For example,materials prepared using aluminum hydride were compared to thoseprepared using aluminum nitrate by using X-Ray PhotoelectricSpectroscopy (XPS or ESCA). This analysis allowed the relative number ofsilicon, aluminum and oxygen atoms on the surface to be determined. Thecomposition originating from the AlH₃ treatment exhibited a very highratio of Al/Si atoms on the surface compared to a composition preparedvia Al(NO₃)₃ wet impregnation. These data suggest concentration of theAl atoms on the external surface when AlH₃ is the reactant but not whenAl(NO₃)₃ is the impregnating material. This concept was confirmed byre-analysis of the compositions after they were ground to expose theirinteriors. The ratio of Al/Si was substantially less after grinding inthe AlH₃ /SiO₃ case but about the same or a little higher in theAl(NO₃)₃ /Al₂ O₃ case. The results are summarized below in Table I.

                  TABLE 1                                                         ______________________________________                                        Relative Number of Atoms Detected on Surface by XPS (ESCA)                    AlH.sub.3 /SiO.sub.2.sup.b                                                                         Al(NO.sub.3).sub.3 /SiO.sub.2.sup.b                              20-30                20-30                                            Sample  Mesh     Ground.sup.a                                                                              Mesh   Ground.sup.a                              Treatment                                                                             Particles                                                                              to Powder   Particles                                                                            to Powder                                 ______________________________________                                        Si.sup.c                                                                              100      100         100    100                                       Al       25      9.9         5.0    6.5                                       O       184      164         168    164                                       ______________________________________                                         .sup.a Ground to a fine powder in Argon.                                      .sup.b Impregnated materials were activated in a stream of N.sub.2 in         50° stages to 700° C. The aluminum content of the final         product was about 3.8-4% wt. Davison 57 grade SiO.sub.2 was employed as       the support.                                                                  .sup.c Data normalized to Si = 100.                                      

Benzene and dialkylbenzene are transalkylated to alkylbenzene by contactwith the siliceous catalysts described herein. The dialkylbenzenescontain two alkyl moieties wherein said moieties contain one to aboutthirty, preferably from one to about twenty, carbon atoms. The two alkylmoieties are preferably the same, although they may be mixed.Illustrative examples of suitable dialkylbenzenes are dimethylbenzene,diethylbenzene, diisopropylbenzene, di-n-propylbenzene, dibutylbenzene,didodecylbenzene, methylethylbenzene, methylisopropylbenzene, and thelike.

The catalyst compositions used in the instant process are used intypical fashion, for example, in packed beds, in batch reactors or influidized beds. Reaction temperatures typically range from about 175° C.to about 450° C., preferably from about 200° C. to about 300° C. Thereaction product is subjected to standard separation techniques andproduct alkyl benzenes are separated from unreacted benzene anddialkylbenzene. Unreacted materials may be conveniently recycled.Suitable inert solvents may also be utilized in the instant process,such as for example aliphatic compounds. Excess starting materials canbe utilized for their solvent effects. Reaction pressures are notcritical and they may be atmospheric, superatmospheric orsubatmospheric.

The preparation of the compositions used as catalysts in the process ofthe instant invention and their utilization as catalysts will be furtherdescribed below by the following illustrative embodiments which areprovided for illustration and are not to be construed as limiting theinvention.

ILLUSTRATIVE EMBODIMENTS Composition Preparation

A porous silica gel (Davison Grade 57, surface area of 300 m² /g, porevolume of 1.0 cc/gm and density of 0.4 gm/cc) 20-30 mesh was pretreatedin dry nitrogen at 700° C. for one half an hour. Exposure of the driedsupport to air was avoided. In a glove box with a dry nitrogenatmosphere 5 grams of the dried support was impregnated with a solutionprepared by dissolving 0.4 grams of AlH₃.1/3(Et₂ O) in 8 ml oftetrahydrofuran. The impregnated material was placed in a vycor tube anddry nitrogen passed over the catalyst as the temperature was increasedin 50° C. intervals (15 min. at each temp.) to 700° C. and held at thistemperature for 15 minutes. The finished composition was cooled with anitrogen flow of 40 ml/min.

Similar compositions were prepared using high surface area silica gels(e.g. Davison Grade 03, surface area of 750 m² /g, pore volume of 0.43gm/cc and density of 0.7 g/cc).

Similar compositions were made by activating at 500° to 550° C.

TRANSALKYLATION OF BENZENE AND DIISOPROPYLBENZENE

A catalyst prepared as described above (3.8% wt. added aluminum; DavisonGrade 57, 20-30 mesh silica gel; activated in nitrogen at 700°) was usedto transalkylate benzene and diisopropyl benzene to cumene. Tenmilliliters of catalyst was used in a vycor tube. The feed was benzeneand diisopropyl benzene in a 5:1 molar ratio, pressure was 400 psig andtemperature was 280° C. The LHSV was about 2. After 2 hours a sample wastaken and analyzed as follows: C₃ -1.8% wt; benzene-78.5% wt;diisopropyl benzene-12.4% wt; cumene-6.5% wt; and triisopropylbenzene-0.83% wt.

I claim:
 1. A process for transalkylation of benzene and dialkylbenzeneto alkylbenzene which comprises contacting the benzene and thedialkylbenzene at about 175° to about 450° C. with a catalyst preparedby a process which comprises impregnating a substantially dehydratedamorphorous silica gel with aluminum hydride dissolved in an anhydrous,non-hydroxyl containing organic solvent, drying the impregnated silicato remove the solvent and subsequently heating the impregnated silica ata temperature of about 300° to about 900° C. in a non-oxidizingatmosphere.
 2. The process of claim 1 where in preparing the catalystthe impregnated silica is subsequently heated to a temperature of about450° C. to about 750° C.
 3. The process of claim 1 where in preparingthe catalyst the impregnated silica before heating contains from about0.01 to about 35 percent by weight of aluminum hydride measured asaluminum metal.
 4. The process of claim 1 where in preparing thecatalyst the impregnated silica before heating contains from about 0.1to about 25 percent by weight of aluminum hydride measured as the metal.5. The process of claim 1 where in preparing the catalyst theimpregnated silica before heating contains from about 1 to about 10percent by weight of aluminum hydride measured as the metal.
 6. Theprocess of claim 5 where in preparing the catalyst the aluminum hydrideis AlH₃.1/3(CH₃ CH₂)₂ O dissolved in tetrahydrofuran or diethyl ether.7. The process of claim 2 where in preparing the catalyst theimpregnated silica before heating contains from about 0.01 to about 35percent by weight of aluminum hydride measured as the metal.
 8. Theprocess of claim 2 where in preparing the catalyst the impregnatedsilica before heating contains from about 0.1 to about 25 percent byweight of aluminum hydride measured as the metal.
 9. The process ofclaim 2 where in preparing the catalyst the impregnated silica beforeheating contains from about 1 to about 10 percent by weight of aluminumhydride measured as the metal.
 10. The process of claim 9 where inpreparing the catalyst the aluminum hydride is AlH₃.1/3(CH₃ CH₂)₂ Odissolved in tetrahydrofuran or diethyl ether.
 11. The process of claim1 wherein the temperature ranges from about 200° C. to about 300° C.